1. Field of the Invention
The present invention relates to a package for a resin-shield type semiconductor device, particularly a premold type semiconductor package, and a process for producting the same.
2. Description of the Related Art
In general, the resin-shield type semiconductor device is produced by mounting a semiconductor chip in a chip-mounting area of a lead frame, then electrically connecting the semiconductor chip to leads by wires, and thereafter, shielding the semiconductor chip with resin.
Alternatively, there is a so-called premold type package wherein a molded body having a recessed chip-mounting area is preliminarily formed by an insert molding of a lead frame. According to this package, a semiconductor chip is mounted in the chip-mounting area, then circuit patterns around the chip-mounting area are electrically connected to the semiconductor chip, and thereafter, the chip-mounting area is covered with a lid, resulting in a semiconductor device.
Nowadays, the latter package of a simple structure has been widely employed in various uses because it is improved in air-tightness due to the advancement of a passivation film on the semiconductor chip itself and/or an adhesive for sealing between the lid and the molded package.
FIG. 5 illustrates a diagrammatic sectional view of the latter package wherein reference numerals 10 and 12 denote a lead frame and a molded body, respectively. This package is provided as a package in which the lead frame 10 is integral with the molded body 12. A semiconductor chip 16 is mounted in a recessed chip-mounting area 14, and electrically connected to the lead frame 10 by wires 18. Then, the chip-mounting area 14 is covered by a lid 20 which is bonded with an adhesive 25 to shield the semiconductor chip 16. The resultant assembly is used as a DIP type or gull-wing type semiconductor device.
The prior art package wherein the lead frame is used, however, has the following problems:
Although the package of this type is simple in structure, it necessitates a process for removing a dam bar (not shown) which is provided for preventing resin from flowing into the spaces between adjacent leads, after the molded body 12 has been molded by a transfer or injection molding process, and further removing resinous flash flowing into spaces between adjacent lead portions extending to the dam bar as in a conventional resin-shield type semiconductor device. This makes the production thereof troublesome.
In addition, a die for cutting the dam bar is expensive and requires a long manufacturing time to result in the increase of the package production cost.
Also, while external leads 10b must be subjected to a forming process to be of a DIP type or a gull-wing type, a die used for such forming is expensive, which is one of factors of the increase of package production cost.
When handling the package for the purpose, for example, of transportation after the external leads 10b have been formed to have a predetermined shape, the external lead 10b is liable to deform because it is supported in a cantilever manner, which is one of factors in a short-circuit accident.
Further, since the external leads 10b extend outward from a body of the package, a total size of the package becomes larger by the length of the external leads 10b, which does not satisfy the requirement for compactness.
On the other hand, a semiconductor device is disclosed in a prior patent application of the present Applicant (Japanese Unexamined Patent Publication No. 5-283460), wherein a base film 50 provided with circuit patterns (lead patterns 52) on the upper surface of a film-like resin substrate is used for compacting the package. That is, as shown in FIG. 6, the lead patterns 52 are provided on the upper surface of the insulating base film 50 and through-holes 54 are provided in the base film 50 so that intermediate portions of the lead pattern 52 are exposed from the base film 50, wherein solder bumps 56 are formed to be projected downward from the exposed lead patterns 52 through the base film 50. Thereby, it is possible to connect the lead patterns 52 with connector pads on the substrate via the solder bumps 56 without the external leads. Thus, the semiconductor device can be smaller in size.
This prior art invention, however, has been made on the premise that the base film 50 is used and the resin-molding is not carried out, which means that a lead frame and a resin-molding technology capable of forming desirable circuit patterns in a stable manner at a lower cost is not usable.